In the field of metal packaging, closures are known having the general form of a metal annular ring component with a sealing panel to which is bonded a lid of peelable lidding material. Radially outwards of the sealing panel, the annular component extends first upwardly to define a chuck wall and then outwardly to define a seaming panel. The seaming panel enables the annular component to be seamed to the edge of a container body. Such closures are commonly used to close container bodies for food products requiring sterilisation in a retort. The sterilisation process subjects the container to high temperatures (typically up to around 130° C.) to ensure that the food within the container is stable for long-term storage and transport. The heating from the sterilisation process produces a consequent increase in pressure inside the container—a positive differential pressure. This positive differential pressure has to be sustained by the lidding material and its bond with the sealing panel of the annular component. The severity of the differential pressure “seen” by the bond is dependent upon whether a retort with balanced overpressure capability is used or not, because balanced overpressure helps to minimise the difference between the pressure inside the container to the pressure outside the container. For the avoidance of doubt, by “positive differential pressure” is meant where the pressure inside the container is greater than that outside the container, and by “negative differential pressure” is meant where the pressure inside the container is less than that outside the container.
EP 0683110 A (CARNAUDMETALBOX SA) 22 Nov. 1995 discloses a container having a closure with a sealing panel inclined relative to a horizontal plane. A lid of peelable lidding material is bonded to the sealing panel. The sealing panel inclination is fixed. When the container of EP0683110A is subjected to a positive differential pressure, the lid tends to dome outwardly. Having the sealing panel inclined at an angle consistent with the doming of the lid where the lid meets the radial inner edge of the sealing panel ensures that the bond between the lid and sealing panel is predominantly loaded in shear rather than in peel when subjected to the positive differential pressure. This therefore avoids the lid progressively peeling itself away from the sealing panel during sterilisation—a phenomenon known as “peelback”. However, whilst having a fixed inclined sealing panel provides optimum performance during sterilisation, it does make the lid harder for a consumer to remove.
EP 2055641 A (IMPRESS METAL PACKAGING S.A.) 6 May 2009 discloses a closure in the form of a lid ring having radial outer and inner portions 2a, 2b (see FIG. 1 taken from EP2055641A). The radial inner portion 2b defines a sealing panel to which a foil lid 3 is bonded. The radial outer portion 2a has a wall that extends first upwardly from the junction with the sealing panel and then outwardly to define a seaming panel. A circumferential score line 30 is provided at the junction between the radial outer and inner portions 2a, 2b and, in effect, defines a “corner score”. The junction between the radial outer and inner portions 2a, 2b defines a natural hinge, with the circumferential score line 30 improving the ability of the radial inner portion 2b to tilt about this hinge in response to differential pressures acting on the foil lid 3. The sealing panel inclination is intended to be able to adapt in response to changes in the differential pressure “seen” by the foil lid 3.
The present invention seeks to provide an alternative closure which provides improved performance to that disclosed in EP2055641A.